This invention relates generally to the field of video displays, and more particularly to an arrangement employed therein to detect and control generation of unwanted emissions.
It is well known that electronic circuitry comprising image display apparatus can exhibit electronic characteristics which generate unwanted signal components that can degrade the displayed image or acoustic output signal. Many methods are known for linearizing circuit operation or reducing harmonic generation to prevent impairment of the audio or visual performance of the device. However, these efforts are directed to the prevention of degraded display performance with little or no regard to unwanted or unintentional emissions emanating from the display device.
A recently introduced Federal Communications Commission rule, 47 CFR xc2xa715 subpart B, Unintentional Radiators, mandates levels of radiation for various electronic products including, for example, TV broadcast receivers, TV interface devices, cable system terminal devices, other receivers, personal computers and peripheral equipment. Specifically, all TV broadcast receivers offered for sale in the United States must comply with section rule 47 CFR xc2xa715.117.
Although engineering efforts have been directed to the improvement of display image quality by the elimination of spurious image degrading artifacts, the desire to achieve the enhanced performance provided by the ATSC standards requires, among other things, wider circuit bandwidth and with attendant high frequency signal currents and voltages. Such wider bandwidth signals, while necessary to provide the desired level of enhanced performance, can unfortunately and inherently result in unintentional emissions with levels greater than those mandated by the FCC.
Unintentional emissions are controlled responsive to the spectral content of the display signal. A video display apparatus comprises a cathode ray tube responsive to a video signal. A processor controls a bandwidth of the video signal coupled to the cathode ray tube in response to an emission control signal. A generating means is coupled to the processor for generating the emission control signal responsive to a component of the video signal.